Composite positive electrode material and preparation method and application thereof

Abstract

The invention belongs to the technical field of batteries, and provides a composite positive electrode material and a preparation method and application thereof.The composite positive electrode material comprises a lithium supplement agent inner core, the surface of the lithium supplement agent inner core is provided with a main body positive electrode material, and the main body positive electrode material comprises at least two doped metal elements; and a high-entropy alloy coating layer is arranged on the surface, far away from the lithium supplement agent core, of the main body positive electrode material. According to the composite positive electrode material disclosed by the invention, the lithium loss problem is effectively reduced by constructing the lithium supplement agent core, the multi-metal doping main body and the high-entropy alloy coating structure, and the high-rate performance and the long-cycle performance of the material can be effectively improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries and relates to a composite positive electrode material and a preparation method and application thereof. Background Art

[0002] As a type of energy storage system, lithium-ion batteries, with their high energy density, long cycle life, and lack of memory effect, have found widespread application in communications, portable electronic devices, electric vehicles, and smart grids. In particular, lithium-ion batteries are considered the optimal choice for electric vehicles (EVs) and large-scale energy storage systems for years to come. With the growing global demand for clean energy and the rapid expansion of the electric vehicle market, the need for high-performance, low-cost battery materials is becoming increasingly urgent.

[0003] Lithium iron phosphate (LiFePO4, LFP), as an important cathode material, is widely used in electric vehicles and large-scale energy storage systems due to its high thermal stability, safety, cost-effectiveness, and long service life. However, despite LFP's many advantages, its low conductivity, poor high-rate performance, capacity fading, and cycling stability remain key bottlenecks restricting its further development. These issues limit the use of LFP in some application scenarios.

[0004] In order to solve the above problems, researchers have proposed a series of improvement strategies, including doping modification, surface coating, crystal structure adjustment, alloying and other methods. These technologies aim to improve the electrochemical properties of LFP materials through physical or chemical means and enhance their practical application value. For example, doping technology usually optimizes the conductivity and electrochemical performance of batteries by adding transition metal elements (such as cobalt, nickel, titanium, aluminum, etc.); surface coating technology mainly uses carbon, oxide or metal materials to enhance the conductivity, stability and rate performance of materials.

[0005] However, while doping technology can improve some of the material's performance, the current practice of doping with a single metal element or a few metal elements has limited improvements in conductivity and cycling performance, particularly under high-rate discharge conditions. On the other hand, while traditional carbon coating and metal oxide coating methods can enhance lithium iron phosphate's conductivity, they often face issues such as uneven coating thickness and poor contact with the substrate material, which in turn affects the coating's actual performance. In particular, under high-rate discharge conditions, the coating's superior performance is difficult to fully realize.

[0006] In addition to focusing on improving the performance of the positive electrode material itself, practical applications also need to consider problems that may arise during long-term service of the positive electrode material, such as lithium loss. Lithium loss not only affects the overall performance of the battery, but may also lead to instability in the lithium replenishment process, further affecting the battery's service life. Existing lithium replenishment methods mainly include the use of lithium source additives or through material modification, but in actual operation, these methods often face problems such as unstable lithium replenishment effects, possible performance degradation, or structural instability caused by excessive lithium replenishment.

[0007] In summary, to meet growing energy demands and promote the development of electric vehicles and large-scale energy storage systems, in-depth research is necessary to effectively improve the performance of lithium iron phosphate materials, particularly addressing their low conductivity, poor high-rate performance, capacity fade, and cycling stability. Furthermore, the development of more efficient and stable lithium replenishment technologies is also necessary to ensure the stability and reliability of batteries over the long term. Summary of the Invention

[0008] In view of the problems existing in the prior art, the present invention aims to provide a composite cathode material, its preparation method, and use. The composite cathode material comprises a lithium supplement core, a main cathode material having at least two doped metal elements on its surface, and a high-entropy alloy coating on the surface of the main cathode material away from the lithium supplement core. By constructing a structure comprising a lithium supplement core, a multi-metal doped main cathode material, and a high-entropy alloy coating, the composite cathode material of the present invention effectively reduces lithium loss and improves the material's high-rate performance and long-cycle performance.

[0009] To achieve this object, the present invention adopts the following technical solutions:

[0010] In a first aspect, the present invention provides a composite positive electrode material, which includes a lithium supplement core, the surface of the lithium supplement core having a main positive electrode material, the main positive electrode material having at least two doped metal elements, and the surface of the main positive electrode material away from the lithium supplement core having a high entropy alloy coating layer.

[0011] The present invention effectively reduces the problem of lithium loss in the main positive electrode material during service by placing the lithium supplement agent as the inner core. In multiple charge and discharge cycles, the capacity decay rate of the battery is significantly slowed down, and the cycle life of the battery is greatly extended. By combining multi-metal doping and high-entropy alloy coating of the main positive electrode material, the conductivity of the material is significantly improved. In particular, during high-rate discharge, it can exhibit higher electrochemical stability and better rate performance than traditional coating materials. Compared with conventional carbon coating or single metal coating, the use of high-entropy alloy coating can provide more uniform and stable conductivity, and has higher thermal stability, thereby improving the safety and stability of the battery in high-temperature environments.

[0012] Specifically, the present invention breaks through the limitations of traditional lithium replenishment, doping, and coating technologies that operate independently through the three-dimensional synergy of in-situ core-shell structure design, dual-element synergistic doping, and high-entropy alloy multifunctional coating. The lithium replenisher core achieves controlled sustained release under the protection of a stable LiFePO4 skeleton doped with at least two doping metal elements (such as Al and Mg), which in turn feeds back to fill the defects of the coating layer; the high-entropy coating layer blocks side reactions and guides the directional migration of lithium ions. The lithium replenisher core and the doped host material can reduce impedance through a chemical bonding interface (Fe-OP). Its sustained-release lithium replenishment characteristics can accurately compensate for lithium loss during the cycle, realizing the integrated synthesis of positive electrode materials and lithium replenishment materials. Unlike existing lithium replenishment technologies, there is no need to add additional additives such as lithium ferrite and lithium nickelate, which reduces costs; the co-doping of metals stabilizes the lattice structure and enhances electron / ion conduction through the charge compensation effect, providing rigid support for the core; the high-entropy alloy coating layer forms a dense multifunctional barrier by virtue of the entropy stabilization effect, inhibiting electrolyte corrosion while establishing a fast lithium ion transmission channel, which is more advantageous than traditional carbon coating. Therefore, the specific closed-loop feedback of doping-coating-lithium replenishment in the present invention forms a self-repairing mechanism, which can significantly improve the overall performance of the material.

[0013] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0014] As a preferred technical solution of the present invention, the core of the lithium supplement agent includes lithium phosphate.

[0015] Preferably, the main positive electrode material includes lithium iron phosphate.

[0016] Preferably, the doping metal elements in the main positive electrode material include at least two of Al, Mg, Zn or Ti.

[0017] Preferably, the doping amount of the doped metal element in the main positive electrode material is 3000-5000 ppm, for example, 3000 ppm, 3300 ppm, 3500 ppm, 3800 ppm, 4000 ppm, 4200 ppm, 4500 ppm, 4800 ppm or 5000 ppm.

[0018] Preferably, the coating metal elements in the high entropy alloy coating layer include at least five of Ni, Co, Mn, Cr, Al, Mg or Zr.

[0019] Preferably, based on the mass of the composite positive electrode material being 100%, the mass of the lithium supplement core accounts for 3% to 5%, for example, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.2%, 4.5%, 4.8% or 5%.

[0020] Preferably, based on the mass of the composite positive electrode material as 100%, the mass proportion of the main positive electrode material is ≥95%, for example, 95%, 95.3%, 95.5%, 95.8%, 96%, 96.2%, 96.5%, 96.8% or 97%, etc.

[0021] Preferably, the thickness of the high entropy alloy coating is 10 to 20 nm, for example, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm or 20 nm.

[0022] In a second aspect, the present invention provides a method for preparing the composite positive electrode material according to the first aspect, the preparation method comprising:

[0023] S1. Providing lithium supplement core;

[0024] S2. The lithium supplement core, the main cathode material raw material and the doping source are mixed, and a hydrothermal reaction and a first calcination are performed in sequence to generate a doped main cathode material and wrap the lithium supplement core to obtain an intermediate;

[0025] S3. The intermediate and the coating source are mixed in liquid phase to obtain a sol, and heat treatment and a second calcination are performed in sequence to generate a high entropy alloy coating layer and coat the main positive electrode material to obtain a composite positive electrode material.

[0026] The main purpose of the hydrothermal reaction in the preparation method of the present invention is to form a coating layer of the main cathode material on the surface of lithium phosphate particles in situ. Taking LFP as an example, during the hydrothermal process, Fe 2+ 、Li + and PO4 3- It is adsorbed on the surface of Li3PO4 particles by electrostatic interaction, forming a local supersaturated layer. The high temperature under hydrothermal conditions promotes the 2+、Li + and PO4 3- Desolvation occurs on the surface of Li3PO4, forming LiFePO4 nuclei. Subsequently, through Ostwald ripening, the small-sized LiFePO4 nuclei dissolve, while large grains continue to grow, ultimately forming a dense coating. Since the particles produced by hydrothermal synthesis are relatively small, the primary purpose of the first calcination is to promote grain growth. The temperature setting should be based on the thermal stability of the material (to avoid decomposition or phase change). This temperature effectively promotes crystallization and particle growth while avoiding excessive particle agglomeration due to excessively high temperatures.

[0027] It's important to emphasize that the coating of the primary cathode material in the preparation method described herein must be performed via an in-situ reaction. The nucleation and growth of the primary cathode material occurs directly on the surface of the lithium supplement, forming a stable chemically bonded interface. Using pre-prepared lithium iron phosphate cathode material for coating results in poor coating, with some cores lacking the coating layer, leading to high interfacial resistance and impeded lithium ion transport.

[0028] As a preferred technical solution of the present invention, in step S1, the method for preparing the lithium supplement core includes:

[0029] According to the stoichiometric ratio of lithium phosphate, the first phosphorus source and the first lithium source are mixed in water, the pH is adjusted, and then heating precipitation reaction, filtering, washing, drying and sintering are carried out in sequence to generate lithium phosphate and obtain the lithium supplement agent core.

[0030] Preferably, the first phosphorus source comprises NaH2PO4.

[0031] Preferably, the first lithium source comprises LiCl.

[0032] Preferably, the pH range for adjusting the pH is 8 to 9, such as 8, 8.1, 8.2, 8.3, 8.4, 8.5, 8.6, 8.7, 8.8, 8.9 or 9.

[0033] Preferably, the temperature of the heating precipitation reaction is 85-95°C, for example, 85°C, 88°C, 90°C, 92°C or 95°C, and the time is 2-4h, for example, 2h, 2.3h, 2.5h, 2.8h, 3h, 3.2h, 3.4h, 3.6h, 3.8h or 4h.

[0034] Preferably, the sintering temperature is 500-700°C, for example, 500°C, 530°C, 550°C, 580°C, 600°C, 620°C, 650°C, 680°C or 700°C, and the sintering time is 1-3h, for example, 1h, 1.31h, 5h, 1.8h, 2h, 2.2h, 2.5h, 2.8h or 3h.

[0035] As a preferred technical solution of the present invention, in step S2, when the main positive electrode material includes lithium iron phosphate, the main positive electrode material raw materials include a second phosphorus source, a second lithium source, an iron source and a carbon source.

[0036] Preferably, the second phosphorus source comprises (NH4)2HPO4.

[0037] Preferably, the second lithium source comprises LiOH·H 2 O and / or Li 2 CO 3 .

[0038] Preferably, the iron source includes FeCl3·6H2O and / or Fe(NO3)3.

[0039] Preferably, the carbon source comprises glucose and / or sucrose.

[0040] As a preferred technical solution of the present invention, in step S2, the second phosphorus source and the second lithium source are first mixed in liquid phase, and the pH is adjusted to 9 to 10, for example, 9, 9.1, 9.2, 9.3, 9.4, 9.5, 9.6, 9.7, 9.8, 9.9 or 10, and then the lithium supplement core, iron source, carbon source and doping source are added and mixed;

[0041] Preferably, the doping source includes a chloride salt corresponding to the doping metal element.

[0042] As a preferred technical solution of the present invention, in step S2, the temperature of the hydrothermal reaction is 160-200°C, for example, 160°C, 170°C, 180°C, 190°C or 200°C, and the time is 6-10h, for example, 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9h, 9.5h or 10h, etc.

[0043] The present invention can regulate the amount of the main positive electrode material formed by adjusting the amount of the main positive electrode material raw material and the parameters of the hydrothermal reaction, preferably maintaining its mass proportion at more than 95%.

[0044] Preferably, after the hydrothermal reaction is completed, filtration and washing are performed first, and then the first calcination is performed.

[0045] Preferably, the temperature of the first calcination is 500-700°C, for example, 500°C, 530°C, 550°C, 580°C, 600°C, 620°C, 650°C, 680°C or 700°C, and the time is 3-5h, for example, 3h, 3.3h, 3.5h, 3.8h, 4h, 4.2h, 4.5h, 4.8h or 5h, etc.

[0046] As a preferred technical solution of the present invention, in step S3, the coating source includes a chloride salt corresponding to the coating metal element.

[0047] Preferably, the coating source is first mixed with a surfactant in liquid phase, and then added to the intermediate for mixing, and then subjected to a sol treatment.

[0048] Preferably, the surfactant comprises polyvinylpyrrolidone (PVP).

[0049] Preferably, the sol treatment process includes adjusting the pH to 8.5 to 9.5 with stirring, for example, 8.5, 8.6, 8.7, 8.8, 8.9, 9, 9.1, 9.2, 9.3, 9.4 or 9.5.

[0050] As a preferred technical solution of the present invention, in step S3, the temperature of the heat treatment is 50-70°C, for example, 50°C, 53°C, 55°C, 58°C, 60°C, 63°C, 65°C, 68°C or 70°C, and the time is 1-3h, for example, 1h, 1.31h, 5h, 1.8h, 2h, 2.2h, 2.5h, 2.8h or 3h, etc.

[0051] Preferably, the temperature of the second calcination is 500-700°C, for example, 500°C, 530°C, 550°C, 580°C, 600°C, 620°C, 650°C, 680°C or 700°C, and the time is 3-5h, for example, 3h, 3.3h, 3.5h, 3.8h, 4h, 4.2h, 4.5h, 4.8h or 5h, etc.

[0052] In the present invention, by adjusting the amount of coating source, the amount of surfactant and the parameters of the heat treatment, the thickness of the high entropy alloy coating layer can be precisely controlled. It is understood that the high entropy alloy coating layer formed by the second calcination of the present invention is an oxide.

[0053] In a third aspect, the present invention provides a battery comprising the composite positive electrode material described in the first aspect.

[0054] Compared with the existing technical solutions, the present invention has at least the following beneficial effects:

[0055] The present invention effectively reduces the problem of lithium loss in the main positive electrode material during service by placing the lithium supplement agent as the inner core. In multiple charge and discharge cycles, the capacity decay rate of the battery is significantly slowed down, and the cycle life of the battery is greatly extended. By combining multi-metal doping and high-entropy alloy coating of the main positive electrode material, the conductivity of the material is significantly improved. In particular, during high-rate discharge, it can exhibit higher electrochemical stability and better rate performance than traditional coating materials. Compared with conventional carbon coating or single metal coating, the use of high-entropy alloy coating can provide more uniform and stable conductivity, and has higher thermal stability, thereby improving the safety and stability of the battery in high-temperature environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 It is a schematic flow chart of the method for preparing the composite positive electrode material in Example 1. DETAILED DESCRIPTION

[0057] The technical solution of the present invention is further illustrated below through specific implementation methods.

[0058] It should be apparent to those skilled in the art that the embodiments are only intended to help understand the present invention and should not be considered as specific limitations of the present invention.

[0059] Example 1

[0060] This embodiment provides a composite positive electrode material, which includes a lithium replenisher core, which is lithium phosphate (Li3PO4); the surface of the lithium replenisher core has a main positive electrode material, which is lithium iron phosphate and has two doped metal elements, Al and Mg, and the surface of the main positive electrode material away from the lithium replenisher core has a high entropy alloy coating layer, which is a composite oxide (oxide alloy) of five coating metal elements, Ni, Co, Mn, Cr, and Al; based on the mass of the composite positive electrode material as 100%, the mass of the lithium replenisher core accounts for 4%, and the mass of the main positive electrode material accounts for 95%; the thickness of the high entropy alloy coating layer is 15 nm.

[0061] The preparation method of the composite positive electrode material is as follows Figure 1 As shown, the preparation method includes:

[0062] S1. Preparation of the lithium supplement core: Add 2.54g (about 0.06mol) of the first lithium source LiCl and 2.40g (about 0.02mol) of the first phosphorus source NaH2PO4 to 100mL of deionized water and stir evenly. Adjust the pH of the solution to 8.5 with ammonia water, maintain the solution at 90°C, and heat and precipitate the solution for 3 hours under stirring to precipitate Li3PO4. The precipitate is then filtered, washed three times with deionized water, dried, and sintered at 600°C for 2 hours to generate the Li3PO4 core, thus obtaining the lithium supplement core.

[0063] S2. Synthesis of the main cathode material by hydrothermal method: first, 4.06g of the second phosphorus source (NH4)2HPO4 was dissolved in water, and then 2.36g of the second lithium source LiOH·H2O was added, and then the pH was adjusted to 9.4 to inhibit the dissolution of the added lithium phosphate; then 0.3g of the lithium supplement core was added and dispersed, followed by adding 9g of the iron source FeCl3·6H2O, 0.1g of the doping source AlCl3·6H2O, 0.08g of the doping source MgCl2·6H2O and 1g of the carbon source glucose, and stirred evenly; the solution was transferred to a hydrothermal reactor, sealed and hydrothermally reacted at 180°C for 8h, so that the lithium iron phosphate was uniformly crystallized on the outer surface of the lithium supplement core; after the reaction was completed, the sample was taken out, filtered and washed with deionized water several times, and then calcined at 600°C for 4h to remove residual NH 4+ and organic matter to form the main cathode material, obtaining an intermediate with an outer layer of LiFePO4 and an inner core of Li3PO4;

[0064] S3. High entropy alloy coating: 0.01 mol each of coating sources nickel chloride, cobalt chloride, manganese chloride, chromium chloride, and aluminum chloride were added to 50 mL of deionized water to obtain a uniform metal precursor solution. 1.5 g of surfactant polyvinyl pyrrolidone was added to the solution to help the metal salts to be evenly dispersed and prevent the particles from agglomerating. The intermediate was then added to the metal precursor solution and stirred evenly to ensure that the alloy solution evenly wetted the surface. The pH value of the solution was adjusted to 9 with ammonia water to promote the hydrolysis of the metal salts to form a sol. The sol mixture was transferred to an oven at 60°C and subjected to low-temperature heat treatment for 2 hours. It was then transferred to a tubular furnace and calcined for a second time at 600°C for 4 hours to form a stable high-entropy alloy (HEA) outer layer coating.

[0065] Example 2

[0066] This embodiment provides a composite positive electrode material. The preparation method of the composite positive electrode material is adjusted by adjusting the amount of the lithium supplement core in step S2, so that the mass proportion of the lithium supplement core in the composite positive electrode material is adjusted from 4% to 1%, and the mass proportion of the main positive electrode material is adjusted from 95% to 98%. Except for the above, other conditions are exactly the same as those in Example 1.

[0067] Example 3

[0068] This embodiment provides a composite positive electrode material. The preparation method of the composite positive electrode material is adjusted by adjusting the amount of the lithium supplement core in step S2, so that the mass proportion of the lithium supplement core in the composite positive electrode material is adjusted from 4% to 3%, and the mass proportion of the main positive electrode material is adjusted from 95% to 96%. Except for the above, other conditions are exactly the same as those in Example 1.

[0069] Example 4

[0070] This embodiment provides a composite positive electrode material. The preparation method of the composite positive electrode material is adjusted by adjusting the amount of the lithium supplement core in step S2, so that the mass proportion of the lithium supplement core in the composite positive electrode material is adjusted from 4% to 5%, and the mass proportion of the main positive electrode material is adjusted from 95% to 94%. Except for the above, other conditions are exactly the same as those in Example 1.

[0071] Example 5

[0072] This embodiment provides a composite positive electrode material. The preparation method of the composite positive electrode material is adjusted by adjusting the amount of the lithium supplement core in step S2, so that the mass proportion of the lithium supplement core in the composite positive electrode material is adjusted from 4% to 6%, and the mass proportion of the main positive electrode material is adjusted from 95% to 93%. Except for the above, other conditions are exactly the same as those in Example 1.

[0073] Example 6

[0074] This embodiment provides a composite positive electrode material. The preparation method of the composite positive electrode material is adjusted by adjusting the amount of the coating source in step S3 so that the thickness of the high entropy alloy coating layer in the composite positive electrode material is adjusted from 15 nm to 5 nm. Except for the above, other conditions are exactly the same as those in Example 1.

[0075] Example 7

[0076] This embodiment provides a composite positive electrode material. The preparation method of the composite positive electrode material is adjusted by adjusting the amount of the coating source in step S3 so that the thickness of the high entropy alloy coating layer in the composite positive electrode material is adjusted from 15 nm to 10 nm. Except for the above, other conditions are exactly the same as those in Example 1.

[0077] Example 8

[0078] This embodiment provides a composite positive electrode material. The preparation method of the composite positive electrode material is adjusted by adjusting the amount of the coating source in step S3 so that the thickness of the high entropy alloy coating layer in the composite positive electrode material is adjusted from 15 nm to 20 nm. Except for the above, other conditions are exactly the same as those in Example 1.

[0079] Example 9

[0080] This embodiment provides a composite positive electrode material. The preparation method of the composite positive electrode material is adjusted by adjusting the amount of the coating source in step S3 so that the thickness of the high entropy alloy coating layer in the composite positive electrode material is adjusted from 15 nm to 30 nm. Except for the above, other conditions are exactly the same as those in Example 1.

[0081] Comparative Example 1

[0082] This comparative example provides a positive electrode material. In the preparation method of the positive electrode material, no lithium supplement core is prepared and no lithium supplement core is used. Except for the above, other conditions are exactly the same as those in Example 1.

[0083] Comparative Example 2

[0084] This comparative example provides a positive electrode material. In the preparation method of the positive electrode material, only one doping source, AlCl3·6H2O, is used in step S2, and MgCl2·6H2O is replaced by AlCl3·6H2O. Except for the above, other conditions are exactly the same as those in Example 1.

[0085] Comparative Example 3

[0086] This comparative example provides a positive electrode material. In step S2 of the preparation method of the positive electrode material, no doping source is used, and the main positive electrode material is not doped. Except for the above, other conditions are exactly the same as those in Example 1.

[0087] Comparative Example 4

[0088] This comparative example provides a positive electrode material. In the preparation method of the positive electrode material, only one coating source, aluminum chloride, is used in step S3, and other coating sources are replaced by aluminum chloride. Except for the above, other conditions are exactly the same as those in Example 1.

[0089] The positive electrode materials obtained in the examples and comparative examples were made into positive electrode sheets, which were assembled into batteries. Each battery was tested. The battery manufacturing method and performance test were based on GB / T 42161-2022 "Test method for first discharge specific capacity and first charge and discharge efficiency of lithium iron phosphate electrochemical performance test". The specific results are shown in Table 1.

[0090] Table 1

[0091]

[0092] As can be seen from Table 1:

[0093] Comparing Example 1 with Comparative Examples 1-4, it was found that in Comparative Example 1, due to the absence of a lithium supplement core, the capacity was not high and the retention rate was significantly reduced; in Comparative Examples 2 and 3, only single doping or no doping was not conducive to the construction of fast lithium ion channels, and the rate performance was hindered; in Comparative Example 4, only single coating had insufficient mechanical strength, and it was easy to break after volume change and produce side reactions with the electrolyte.

[0094] Comparing Example 1 with Examples 2-5, it was found that in Example 2, since the amount of lithium supplement was insufficient relative to that in Example 1, the initial lithium compensation was limited and the capacity was low; the proportion of the lithium supplement agent core was optimal when it was 3% to 4%, the lithium supplement agent provided a stable lithium source, suppressed capacity decay, and had the highest retention rate; in Example 5, the lithium supplement agent core, which was in excess relative to Example 1, occupied the volume of the active material, and inactive components may remain due to incomplete reaction, resulting in a decrease in capacity; at the same time, lithium was continuously lost during the cycle of Example 2, the capacity decayed rapidly, and the retention rate was low, while in Examples 4-5, excessive lithium supplement agent led to structural stress or side reactions, and the cycle stability decreased; in Examples 2 and 3, the lithium supplement agent was less, had little effect on ion / electron transport, and had better rate performance. In Examples 4 and 5, excessive lithium supplement agent increased the interface impedance, hindered lithium ion diffusion, and significantly reduced the rate performance.

[0095] By comparing Example 1 with Examples 6-9, it was found that the thickness of the high-entropy alloy coating needs to strike a balance between protection (suppressing side reactions) and ion transfer efficiency (reducing impedance). At 15 nm, the entropy stabilization effect of the high-entropy coating and the nanoscale grain boundary design achieve optimal synergy; in Example 6, its high-entropy alloy coating is too thin relative to Example 1, and the volume change of Li3PO4 during the cycle may cause the coating to rupture, the electrolyte penetration triggers continuous side reactions, and the capacity retention rate is significantly reduced; in Examples 8 and 9, the alloy layer that is too thick relative to Example 1 significantly increases the interfacial impedance, the lithium ion migration rate decreases, the capacity decreases, the polarization is aggravated at high rates, and the capacity retention rate drops sharply.

[0096] In summary, the present invention breaks through the limitations of traditional lithium replenishment, doping, and coating technologies that operate independently through the three-dimensional synergy of in-situ core-shell structure design, dual-element synergistic doping, and high-entropy alloy multifunctional coating. The lithium replenisher core achieves controlled sustained release under the protection of a stable LiFePO4 skeleton doped with at least two doping metal elements (such as Al and Mg), which in turn feeds back to fill the defects of the coating layer; the high-entropy coating layer blocks side reactions and guides the directional migration of lithium ions. The lithium replenisher core and the doped host material can reduce impedance through a chemical bonding interface (Fe-OP). Its sustained-release lithium replenishment characteristics can accurately compensate for lithium loss during cycling, realizing the integrated synthesis of positive electrode materials and lithium replenishment materials. Unlike existing lithium replenishment technologies, there is no need to add additional additives such as lithium ferrite and lithium nickelate, which reduces costs; the co-doping of metals stabilizes the lattice structure and enhances electron / ion conduction through the charge compensation effect, providing rigid support for the core; the high-entropy alloy coating layer forms a dense multifunctional barrier by virtue of the entropy stabilization effect, inhibiting electrolyte corrosion while establishing a fast lithium ion transmission channel, which is more advantageous than traditional carbon coating. Therefore, the specific closed-loop feedback of doping-coating-lithium replenishment in the present invention forms a self-repairing mechanism, which can significantly improve the overall performance of the material.

[0097] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the scope of protection of the present invention.

[0098] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0099] In addition, the various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A composite positive electrode material, characterized in that The composite positive electrode material includes a lithium supplement core, the surface of the lithium supplement core has a main positive electrode material, the main positive electrode material has at least two doped metal elements, and the surface of the main positive electrode material away from the lithium supplement core has a high entropy alloy coating layer.

2. The composite cathode material according to claim 1, characterized in that The lithium supplement core includes lithium phosphate; Preferably, the main cathode material includes lithium iron phosphate; Preferably, the doping metal elements in the main positive electrode material include at least two of Al, Mg, Zn or Ti; Preferably, the doping amount of the doping metal element in the main positive electrode material is 3000 to 5000 ppm; Preferably, the coating metal elements in the high entropy alloy coating layer include at least five of Ni, Co, Mn, Cr, Al, Mg or Zr; Preferably, based on the mass of the composite positive electrode material being 100%, the mass of the lithium supplement core accounts for 3% to 5%; Preferably, based on the mass of the composite positive electrode material being 100%, the mass of the main positive electrode material accounts for ≥95%; Preferably, the thickness of the high entropy alloy coating is 10 to 20 nm.

3. A method for preparing the composite positive electrode material according to claim 1 or 2, characterized in that: The preparation method comprises: S1. Providing lithium supplement core; S2. The lithium supplement core, the main cathode material raw material and the doping source are mixed, and a hydrothermal reaction and a first calcination are performed in sequence to generate a doped main cathode material and wrap the lithium supplement core to obtain an intermediate; S3. The intermediate and the coating source are mixed in liquid phase to obtain a sol, and heat treatment and a second calcination are performed in sequence to generate a high entropy alloy coating layer and coat the main positive electrode material to obtain a composite positive electrode material.

4. The method for preparing a composite positive electrode material according to claim 3, wherein: In step S1, the method for preparing the lithium supplement core includes: According to the stoichiometric ratio of lithium phosphate, a first phosphorus source and a first lithium source are mixed in water, the pH is adjusted, and then heating precipitation reaction is carried out in sequence, followed by filtering, washing, drying and sintering to generate lithium phosphate and obtain a lithium supplement core; Preferably, the first phosphorus source comprises NaH2PO4; Preferably, the first lithium source comprises LiCl; Preferably, the pH range of the pH adjustment is 8 to 9; Preferably, the temperature of the heating precipitation reaction is 85-95°C and the time is 2-4 hours; Preferably, the sintering temperature is 500-700° C., and the sintering time is 1-3 hours.

5. The method for preparing a composite positive electrode material according to claim 3 or 4, characterized in that: In step S2, when the main cathode material includes lithium iron phosphate, the main cathode material raw materials include a second phosphorus source, a second lithium source, an iron source and a carbon source; Preferably, the second phosphorus source comprises (NH4)2HPO4; Preferably, the second lithium source comprises LiOH·H2O and / or Li2CO3; Preferably, the iron source comprises FeCl3·6H2O and / or Fe(NO3)3; Preferably, the carbon source comprises glucose and / or sucrose.

6. The method for preparing a composite cathode material according to any one of claims 3 to 5, characterized in that: In step S2, the second phosphorus source and the second lithium source are first mixed in liquid phase, the pH is adjusted to 9-10, and then the lithium supplement core, iron source, carbon source and the doping source are added and mixed; Preferably, the doping source includes a chloride salt corresponding to the doping metal element.

7. The method for preparing a composite cathode material according to any one of claims 3 to 6, characterized in that: In step S2, the hydrothermal reaction temperature is 160-200° C. and the time is 6-10 hours; Preferably, after the hydrothermal reaction is completed, filtration and washing are performed first, and then the first calcination is performed; Preferably, the temperature of the first calcination is 500-700° C., and the time is 3-5 hours.

8. The method for preparing a composite cathode material according to any one of claims 3 to 7, characterized in that: In step S3, the coating source includes a chloride salt corresponding to the coating metal element; Preferably, the coating source is first mixed with a surfactant in liquid phase, then added to the intermediate, mixed, and subjected to a sol treatment; Preferably, the surfactant comprises polyvinylpyrrolidone; Preferably, the sol treatment process includes adjusting the pH to 8.5-9.5 and stirring.

9. The method for preparing a composite cathode material according to any one of claims 3 to 8, characterized in that: In step S3, the heat treatment temperature is 50-70°C and the time is 1-3 hours; Preferably, the second calcination is performed at a temperature of 500-700° C. and for a time of 3-5 hours.

10. A battery, characterized in that: Contains the composite positive electrode material according to claim 1 or 2.

Images